A variety of devices for sensing the presence of train wheels have been previously proposed. These sensing devices include photoelectric devices, mechanical switches, load sensing, proximity switch technologies and magnetic disturbance measuring devices.
Electromagnetic interference is very common in the electrified railway environment, for example AMTRAK, streetcars, and Metro systems. The interference is due primarily to the electromagnetic field that is induced between the power conductor and the return conductor as the locomotive (or Electric Multiple Unit, EMU) draws power. The fields can also radiate from the conductors depending on the grounding.
There is a need for a railway wheel sensor that can operate even when subjected to electromagnetic interference.